The present invention relates to improved polyamide yarn and to an improved fiber finishing process for polyamide yarn in which fiber finish compositions containing a novel blend of antioxidant compounds are applied to the yarn. The yarns of the invention are of particular interest in the production of tire cord and other industrial applications and display unexpected improvement in aging properties, particularly fiber-to-rubber adhesion retention.
Stabilized polyamide compositions incorporating copper compounds together with diarylamine antioxidants into the polymer are disclosed in U.S. Pat. No. 3,113,120 to Papero et al. Such compositions display resistance to deteriorating effects of light, weathering, and heat. Polyamide compositions incorporating an aging inhibitor which is a diphenylamine-acetone condensation product are disclosed in U.S. Pat. No. 3,003,995 to Schule.
Representative finishes for polyamide yarn to be processed into tire cord include U.S. Pat. Nos. 4,129,507 to Marshall et al. and 4,371,658 to Marshall et al. U.S. Pat. No. 3,397,081 to Mayberry discloses a finish composition for nylon tire cord which includes the low temperature reaction product of diphenylamine and acetone. U.S. Pat. No. 4,469,606 to Reid et al. discloses a fiber treating composition comprising a mixture of a specified triazine together with a multifunctional hindered phenol.
Applicant has discovered that by applying a novel combination of antioxidant compounds to the surface of the polyamide yarn, preferably after drawing, such yarns display unexpected improvement in aging properties, particularly the retention of fiber to rubber adhesion, a property essential to tire cord applications.